How Hard to Scoop Will My Gelato Be? (part I)
On why PAC is not the best tool to estimate scoopability or serving temperature, and what to do about it.
Introduction
In this article we discussed what makes Gelato special and explained that two key factors are its consistency and mouthfeel. Unlike regular ice cream, Gelato has a fluffy, mousse-like consistency that is particularly pleasant on the palate. It also doesn't feel so cold in the mouth.
If you are anything like me (and most people that I know), you only have to look at the image above to oh- so-very-much want to have one. As we discussed in the article, the secret to this is the careful blend of ingredients to achieve the perfect balance of structure and texture, while allowing us to serve our creams at a higher temperature.
The goal is to achieve an equilibrium of parameters that places our gelato in the sweet spot between soft and hard, dry and moist, fluffy and dense. Because you cannot have great Gelato without getting the serving consistency right.
This article will discuss one of the key parameters involved in achieving this.
Read on!
Assessing Hardness
“Know the PAC of thy Gelato and thou shalt know how hard it will be in thy cabinet”
In this other article I discussed a widespread tool used to estimate hardness: the ubiquitous PAC (or AFP, or FPDF, or SE). The idea behind PAC is that, by balancing our recipe within certain ranges, we ensure that our Gelati or Sorbetti will be scoopable and at the sweet spot of consistency to delight our cherished patrons.
That's what almost everyone does, so, it got to be right… right?
Well, not so fast. You see, although knowing a recipe's PAC is fundamental to proper balancing, it is actually far from giving a realiable indication of the hardness (or scoopability) of a recipe. Let's have a closer look and you will understand why.
The Shortcomings of PAC, part I
To better understand the shortcomings of PAC, let's have a look at the recipes below. According to the widely accepted rule of thumb in the industry, they should all scoop similarly in a cabinet set at -12ºC, given their PAC ranges.
If you need a reminder from the PAC article, here it goes:
- For Gelati: PAC ÷ 2 = ideal serving temperature for scoopability. In this case ~24 ÷ 2 = 12 → -12ºC
- For Sorbetti: PAC ÷ 2.5 = ideal serving temperature for scoopability. In this case ~30 ÷ 2.5 = 12 → -12ºC
Therefore, according to the rule of thumb, all three creams should scoop reasonably similarly in the cabinet or display.
If you are a tinkerer, go ahead: batch them, keep them in the cabinet at -12ºC and try to scoop them for yourself — you will realise they don't. If you have experience with serving gelato, you will know already that a nut or chocolate cream with the same PAC as a fior di latte will be harder to scoop.
And if you don't tick either box, just trust me — they won't.
Next, did you notice something about the rule of thumb — the fact that there is a different denominator for Gelati than for Sorbetti? If PAC were an effective indicator of scoopability and serving temperature in and of itself, the denominator should be the same for both, right?
If you are asking that question, you are heading in the right direction.
The reason why the difference was introduced is that everyone noticed that with the same PAC and at the same temperature in the cabinet, Sorbetti were considerably harder than Gelati.
But why is that? Let's have a look into what is happening.
The Shortcomings of PAC, part II
One of the factors at play in the PAC paralax between Gelati and Sorbetti is the amount of water in the recipe. Under normal circumstances, water is the only thing that freezes in a mix, so the amount of frozen water in a cream is directly linked to how hard it is — remember, water is soft and ice is hard, so the balance between frozen and liquid water at a given temperature will determine where in the spectrum between liquid and rock solid your cream will be.
Usually Gelati will have 40% total solids (TS), so 60% water; Sorbetti on the other hand, will have 30% TS, so 70% water. And I guess it is easy to see that if we have more water in a recipe, more of the recipe will be liable to freezing, so it will feel harder at a given temperature.
Not so clear? Let's look at it in another way.
Remember that PAC is an indication of the potential of the ingredients to lower the freezing temperature of water? This means that, in a recipe with the same potential but more water, we will have less anti-freezing because the anti-freezing potential is stretched wider. Imagine that you have the equivalent of 240gr of sucrose (PAC 24 in 1,000gr of recipe) to anti-freeze 600gr or 700gr of water. On which one do you think it will be more effective?
The one with less water of course!
So I hope it becomes easy to see why, with the same PAC, a Sorbetto will feel harder than a Gelato at the same temperature — because it will have more frozen water.
And the only conclusion we can come to is that, on its own, PAC (or AFP or FPDF, or SE) cannot be a reliable indicator of a recipe's scoopability or serving temperature.
So… how do we fix that?
Calculating Frozen Water
“Know only the PAC of thy Gelato and thou shalt not know how hard it will be in thy cabinet”
There you go, this slightly rephrased motto is a bit more realistic. It is important to know the PAC of your recipe, but you won't know its scoopability or ideal serving temperature only with that figure.
So what else do we need to know?
The hint is in the section above, when we said that water is the only thing that can freeze in a mix. As it happens, not all water in a mix freezes at once; it is a gradual process, in which only a fraction percentage becomes solid at the freezing point, freezing more and more as the temperature drops further. As a result, there is a range of temperature in which not all water is frozen, so the hardness (and dryness) of the cream will vary.
Put it another way, the consistency of a mix at a given temperature will be largely determined by the amount of frozen water at that given temperature. Makes sense right? Ice is hard, so the more frozen water we have, the harder our Gelato or Sorbetto will be.
Less water frozen = softer cream
More water frozen = harder cream
Great! But… How do I know how much water is frozen in my recipe at a given temperature? And how much frozen water will yield a good consistency?
Well, it turns out that a really clever guy named Pickering spent a lot of time in 1891 figuring out how a sugar-water solution freezes as the temperature goes down, based on the solution concentration. Then another very clever chap named Leighton created some really handy tables in 1927. Armed with these tables and a little bit of Excel formulations we can calculate how much frozen water a recipe will have in a wide temperature range, and with a bit of experimentation, figure out how much frozen water yields our favourite consistency.
But before we get to the calculations, we have to know what parameters to include. We already discussed all of them, but lets just recap:
- The first is the PAC of a recipe: since it indicates its potential to lower the freezing point of water, a higher PAC will result in less frozen water at a given temperature.
2. The second is the percentage of water: a recipe with more water will have a more stretched PAC, which will result in more frozen water at a given temperature. The percentage of water will be 100% - TS% so we need to know the Total Solids (TS) of the recipe.
3. Finally, we will need to know our serving temperature, because it will determine how much of the water in the recipe will be frozen.
Shall we do a quick example with two different recipes to make it clear?
Let's start with the two recipes below, intentionally twisted to have the same PAC:
From the recipes we can extract the parameters for our hardness calculation:
With these numbers at hand we can get to the calculations. The first thing we will do is to determine the Normalised PAC (PACn) of the recipe. This is the recipe's PAC applied over its Total Water (TW), and is a very straight-forward calculation as follows:
Therefore, in our two examples above we will have:
As you can already see, although the recipes have the same PAC, they yield different results due to their different water content. It is clear that the Sorbetto will have more frozen water, because once normalised it has a lower anti-freezing power.
Now that we have the normalised PAC of our recipes, the next step is to find out how much lower is the freezing point of the water in each of them, a.k.a. the recipe's Freezing Point (FD). For that we will use the Leighton table we mentioned earlier:
So in our example, we can extrapolate the following Freezing Point (FP) values:
Fior di latte: approx. -2.5ºC
Lemon sorbetto: approx. -2.0ºC
From the above you can see clearly that the Sorbetto will freeze at a higher temperature than the Fior di latte, which means it will be harder in the freezer at the same temperature (because it will have more frozen water at that same temperature).
And there you go, you can now see clearly that recipes with the same PAC will freeze at different temperatures, which means that one will be harder than the other at the same temperature in the cabinet. So you now understand that PAC alone cannot be representative of hardness in the cabinet or serving temperature — it can only be (at best) a rough guide.
And well done for that, it is a great step forward!
But you might be asking, 'so… what alternative is there to assess hardness?'
This is something we will cover in more detail in the second part of this article — you got a lot to think about with what we have seen so far.
For now, let's say that much more useful than just the PAC would be to know the freezing point (FP) of a recipe, because if two recipes freeze at the same temperature, their hardness would be similar.
If that makes sense to you, don't miss the next episode. I will cover freezing point and how to calculate it, as well as two factors which I think is much more useful in estimating a cream's hardness.
Stay tuned!
Wrapping Up
- PAC (or AFP, or FDPD or SE) is usually regarded as the de facto indicator of display hardness and serving temperature;
- This assumption falls apart at close scrutiny: recipes with the same PAC will freeze at different temperatures so will have different hardness at the same temperature;
- PAC is only an indication of the potential that the ingredients in a recipe have to lower the freezing point of the water contained it. Therefore it is crucial to calculate the recipe's PAC in relation to the amount of water it contains. We call this normalised PAC (PACn);
- Once we know the normalised PAC of a recipe we can calculate its freezing point (FP), which is a much more useful figure, as it relates directly to the amount of ice in the recipe at a given temperature and therefore to its hardness at that temperature.
A presto!!
